Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$91.31	12.572%	$102.7895	$102.79	$102.80	$102.80
Purchase #2	$58.32	7.549%	$62.7226	$62.72	$62.70	$62.70
Purchase #3	$120.69	5.399%	$127.2061	$127.21	$127.20	$127.20
Purchase #4	$235.34	13.106%	$266.1837	$266.18	$266.20	$266.20
Purchase #5	$123.58	8.797%	$134.4513	$134.45	$134.45	$134.50
Purchase #6	$201.44	8.428%	$218.4174	$218.42	$218.40	$218.40
Purchase #7	$216.75	10.213%	$238.8867	$238.89	$238.90	$238.90
7 purchase totals =	$1,047.43		$1,150.6573	$1,150.66	$1,150.65	$1,150.70